1. Field of the Invention
The present invention relates to methods of purifying oils, and more specifically, to an improved method for purifying used lubricating oils.
2. Prior Art
The reliance on petroleum products in industrialized nations is well recognized. This has led many countries, including the United States, to spend substantial sums in terms of exploration and development of oil wells in order to meet the needs of industry. However, notwithstanding such efforts by many countries, the demand for oil continues to outstrip the supply and has led to substantially increased costs of the oil as well as the goods made therefrom. Another factor which adversely effects the supply of oil is the problems of obtaining the oil from the earth without causing damage to the environment. Recent legislation in various countries throughout the world has limited the methods of oil exploration such that the environment is not adversely effected. This too has increased the costs of oil and, in some situations, has decreased the efficiency of operating existing oil wells. In response to this problem, the prior art has disclosed many methods for reprocessing used oil rather than discard it so as to recycle the used oil in an attempt to meet the ever increasing demand for oil. If such recycling methods are relatively effective, the reprocessed oil can be used directly in place of new oil, thus decreasing the demand for new oil.
In one method of treatment which has been used in the prior art, the used oil is first treated with a caustic compound at an elevated temperature to drive off water and to break the various soaps in the oil as well as to neutralize the oil. In the course of heating, the light ends of the oil are flashed off and are generally burned. After the heating procedure, the oil is then cooled and a small quantity of concentrated sulfuric acid is added. After settling, the bottoms are drawn off which contain an acid sludge comprising sulfuric acid, dissolved sulfonates and oxygenated hydrocarbon. This sludge, which may constitute 5 to 20% by weight of the used oil being treated, is disposed of by being placed in a container to prevent the acid fumes from escaping and is then dumped in an appropriate manner. It should be noted, however, that due to the noxious properties of the acid sludge, it is presently very difficult to dispose of such sludge in a manner which is environmentally acceptable. After removal of the acid sludge from the oil, the top oil is then generally heated and finely divided clay is added. The mixture of clay and top oil is then further heated and cooled and finally passed through a filter press. This procedure gives the yield only of about 50% reclaimed oil based on the weight of the used oil originally treated. Moreover the procedure produces large quantities of acid sludge which, as hereinabove described, is difficult to dispose of properly. Finally, the procedure requires substantial heating and other type procedures which add to the expense of such method. This type of method is generally described in U.S. Pat. No. 2,319,598.
Yet another method for treating oil is disclosed by Chambers, et al., U.S. Pat. No. 3,625,881. As a preliminary treatment, Chambers, et. al. pretreat the used oil feedstock to remove substantial quantities of water. This is done by flash vaporization of the feedstock at a temperature below its coking point. After flash evaporation of the feedstock, Chambers, et al. then admix the dried feedstock with concentrated aqueous alkali metal hydroxide and also with additional oil at a temperature of about 200.degree. to 300.degree.. After mixing, the mixture is fed to a centrifuge where a liquid effluent is separated from carbonaceous material in the original feedstock. Thus, it is fair to say that Chambers, et al. method deals primarily with an involved distillation procedure for reclaiming used crankcase oils, which is expensive and time consuming.
A still further method is disclosed by Great Britain Pat. No. 742,909. The British patent is directed to the treatment of a lubricating oil derived from naphthenic crude oil. The process includes the steps of treating the mineral lubricating oils with a aqueous extracting agent and then contacting the treated oil countercurrently in a second zone with water, recovering the washed oil for drying and further refining, and recovering the alcohol from the aqueous extracting agent and collecting the aqueous residue. Because such method contemplates the use of countercurrent mixing, it is at odds with processes, such as that disclosed herein, wherein such countercurrent mixing would work against the settling of the various sludges, soaps and the like. Other further prior art methods of refining crude oil are disclosed in U.S. Pat. No. 2,376,418; U.S. Pat. No. 3,639,229; and U.S. Pat. No. 3,449,243.
As seen from the above methods, while there are many methods which are effective to some extent in the purifying of used lubricating oils, they are relatively expensive, require complex equipment, and produce acid sludges which are difficult to dispose of properly. In response to these problems, two methods have been disclosed which tend to overcome these problems associated with the prior art. These methods are disclosed in U.S. Pat. No. 3,819,508 and U.S. Pat. No. 3,835,035. In the methods disclosed in these patents, the used lubricating oil is mixed with a soluble, predominantly hydrocarbon diluent. The diluted lubricating oil is mixed with a miscible alcohol and water mixture which contains in solution a small amount of either an acid or a base. The diluted lubricating oil-alcohol water mixture is then centrifuged to remove sludge and metal compounds from the oil. Such centrifugation causes the formation of a diluted oil phase and a water-alcohol phase. The problem associated with this type of method is that centrifugation is an expensive process and is the limiting factor on the quantities of oil which can be processed. Moreover, if large quantities of sludge and other undesirable components are contained within the oil, the efficiency of the process decreases and the percent of recoverable oil obtained from centrifugation decreases. The present invention represents an advancement over the two methods discussed hereinabove and contains none of the aforementioned shortcomings associated with the other prior art production methods. The present invention includes unique ordered steps which enables the present method to alleviate the need for centrifugation and thus substantially reduces costs and improves the reliability of equipment associated with all prior art methods. In addition, by the use of the method of the present invention, increased yields are also achieved over many prior art methods.